The overall goal of this program is to contribute to an understanding of the mechanism of interaction between thymus-derived, helper cells (T cells) and bone marrow-derived, precursor cells (B cells) in the antibody response of mice to sheep erythrocytes (Srbc). Detailed study has been made of the optimum priming and elicitation doses of antigen employed in a secondary IgM response induced in recipient mice not all of which possess response units for a primary response. Experiments to elucidate the cell type responsible for this IgM priming are in progress. The secondary response of spleen cells is being examined in diffusion chamber cultures. Spleen cells primed with high and low doses of Srbc are being used. The kinetics of priming by the two doses of Srbc are different as observed in a cell transfer system. Dose-response experiments of the DPFC output of a limiting number of spleen cells as a function of added bone marrow cells have yielded unexpected non-linear relationships. Preliminary studies on the mechanism of antigenic competition show that a soluble factor is involved in mediating suppression.